U.S. space agency engineers say they have tested five of 11 possible movements that might free the Mars rover Spirit, which is trapped in loose martian sand.

Spirit became trapped in April and since then Jet Propulsion Laboratory engineers in California have been using a test rover placed in a specially constructed sand box to simulate how to best extract Spirit.

The most recent maneuver to be evaluated was a crablike backward drive, with all four corner wheels turned 60 degrees toward the right, JPL officials said.

Other maneuvers yet to be evaluated include crabbing backward with wheels turned 20 degrees to the right, a tight forward right arc, a clockwise turn in place, a counterclockwise turn in place and crabbing forward with wheels turned to the left.

The results of the experiments will determine which driving commands will be transmitted to Spirit and they might be a combination of some of the 11 maneuvers being tested, NASA said.